N/A
Glaucoma is one of the leading causes of irreversible blindness worldwide. With early detection, accurate diagnosis and appropriate therapy, the visual loss of glaucoma is largely preventable. Glaucoma is not a single disease, but a large group of disorders sharing optic nerve damage as a common feature. The optic nerve damage is related to the intraocular pressure in most cases and to visual field loss in all cases.
Determination of the anatomic type of glaucoma, namely, xe2x80x9copen anglexe2x80x9d or xe2x80x9cnarrow or closed angle,xe2x80x9d is essential for effective treatment. Differentiation between open and narrow or closed angles must be made before a therapeutic strategy may be devised. Historically, the depth of the anterior chamber has been evaluated by the technique of gonioscopy, in which a lens is coupled to or contacts the cornea, which is uncomfortable for the patient. Direct (Koeppe) gonioscopy also requires the patient to be in a recumbent position. Gonioscopy also requires dexterity to coordinate the patient, lens, microscope and illumination source and experience to-interpret anatomic landmarks. The ancillary technique of B-scan ultrasonography has been used in recent years, but also requires contact with the corneal surface.
The present invention provides a non-invasive measurement system using optical principles to evaluate the anterior chamber depth of a patient""s eye with ease, precision, and accuracy. In a first embodiment, the measurement system interfaces with an existing slit lamp ophthalmology examination table. The measurement system includes a base that mounts securely, either removably or permanently, to the slit lamp table in any suitable manner. An interface to a horizontal drive shaft of the slit lamp travels with the drive shaft in a direction, the Y direction, along the optical axis of the patient""s eye, orthogonal to the axial length of the drive shaft. The interface is mounted to a linearly translatable slide mechanism coupled to a linear measurement device. Thus, as the microscope is moved in the Y direction along the optical axis of the patient""s eye, the interface and the slide mechanism move the same distance.
The linear measurement device, such as a linear encoder, is in communication with suitable circuitry that is operative to translate signals from the linear measurement device to an operator-readable display. The linear measurement device and the display, such as a three- or four-digit LED display, are readily operative to indicate distances to 100 micrometer or 10 micrometer accuracy. The LED display may be set to zero at any time by pushing a suitable button in communication with the LED display.
To make a distance measurement between cornea and iris, the user first finds the location in the eye to be measured using the stereo microscope and joystick control of the slit lamp. Next, the user finds the best focus with the stereo microscope in the plane of the cornea, then pushes the zero button to zero the display. The user next moves the microscope to focus on the surface of the iris or the edge of the pupil. The distance traveled in the Y direction is detected by the measurement system and displayed for the user. The user repeats this measurement procedure on every other location within the eye required for diagnosis. Other distances within the eye may be measured, such as from the cornea to the retina or from the iris or pupil to the retina.
In a further embodiment of the present invention, the measurement system includes a three-axis stage assembly supporting an optical microscope assembly that interfaces with a digital camera and television monitor under the control of a suitably programmed controller or computer. Television frames of the eye are analyzed on the fly to store in memory unique signal signatures associated with in-focus features and their measured location between the cornea and the iris. The system may include an engagement mechanism to engage with an existing slit lamp microscope. Alternatively, the system may be configured as a stand-alone measurement system used solely for making anterior chamber distance measurements.
The present measurement system is non-invasive, requiring no contact with the eye or alteration of the configuration or distortion of the cornea or anterior chamber angle, as gonioscopy or contact ultrasonography do. The present system does not require the use of an anesthetic or a lengthy recuperative period to resume normal visual tasks. The system is fast and simple to use by the doctor and convenient for the patient. It is quantitative and less subject to observer bias and interpretation, interobserver variation or inter-test fluctuation.